.NET Windows Forms in a Nutshell

Extender Providers

Although the Control class provides a very rich set of features, inevitably it cannot be all things to all people. UI innovations continue to emerge, so even if the Control class were to represent the state of the art today, in time, it would inevitably end up looking short on features.

However, Windows Forms provides a very useful way of extending the abilities of the basic Control class. It is possible to place a component on a form that adds a feature to every single control on that form. Such a component is referred to as an extender provider. We will see how to write extender providers in Chapter 9, but no discussion of forms would be complete without looking at how to use them.

The Forms Designer supports extender providers. An extender provider can add new properties to all controls on a form. An example of this in the Windows Forms framework is the ToolTip class. As mentioned in Chapter 2, the Control class does not provide ToolTip support. But this doesn’t matter—the framework has a ToolTip class that is able to augment any control with ToolTip support. If you drop the ToolTip component onto a form, it will appear in the component tray at the bottom of the designer. (All non-UI components appear here; the only kind of component that has any business appearing on the form at design time is a control, so everything else appears in the component tray. And the ToolTip isn’t strictly a UI component; it is a component that modifies the behavior of other controls.) ...